Effects of Formulation on Stability of Spray-Dried Egg

Moisture adsorption isotherms of spray-dried whole egg, microencapsulated with gelatin (G), lactose (L), pullulan (P), and their mixtures at equal ratios (gelatin + lactose [GL] and gelatin +pullulan [GP]), were determined using the standard static-gravimetric method at 25°C. The data were fitted to the various sorption models and the constants were estimated by nonlinear regression analysis. Among the sorption models tested, the Guggenheim-Andersen-de Boer (GAB) and Ferro Fontan equations were recommended for characterizing the adsorption behavior of spray-dried whole egg, either microencapsulated or unencapsulated, in the water activity range of 0.11–0.84. It was indicated that all of the egg powders were stable up to a water activity of 0.43. The oxidative stability of microencapsulated powders was investigated under storage conditions of 20°C and 50% relative humidity (RH). The microencapsulation process resulted in a decrease in the cholesterol oxidation level of egg powder during storage, where it followed a zero-order reaction kinetics and the t rej value representing the time required to reach total cholesterol oxidation products (TCOP) = 384.2 µg/g egg fat as the upper limit of acceptability for fat oxidation was calculated as 1,124 days at 20°C for egg powder microencapsulated with lactose. The relations among glass transition temperatures, oxidation rate constants, and monolayer moisture content values obtained by the GAB model are also highlighted.